Electrolytes

One thing to consideris absorbtion.

Once you pass a certain level of dehydration, drinking only water will not help much.

Dehydration can cause plain water to bypass the gastric lining and pass through your system without being absorbed. All you wind up with is an intestine full of water.

Something like Gatorade wil be much more readily absorbed and rehydrate you.

Even Gatorade is not optimal. There are recipes out there where you can make your own concoction with water, sugar, salt and citrus juice.